Hobbs/Abstract Aerosols may plan an important role in the radiation balance of the atmosphere on local, regional and global scales. Recent estimates suggest that the globally-averaged climate forcing due to the direct effects of anthropogenic sulfate could be similar in magnitude (but opposite in sign) to that produced by anthropogenic "greenhouse" gases. However, there are large uncertainties associated with estimating the aerosol effects. The purpose of this research is to obtain measurements on atmosphere aerosols (with emphasis on those that derive from anthropogenic sources) that will reduce these uncertainties. The proposed research consists of two main activities. (a) Measuring aerosol size distributions, chemical composition, hygroscopic growth factors, light-scattering efficiency, backscattering of solar radiation, and singlescattering albedos in the Pacific Northwest, California, the eastern United States, Alaska and Brazil. (b) Conducting an aerosol "column-closure" experiment off the east coast of the USA. Calculations of the effects of aerosols on solar radiation, based on detailed airborne measurements of the physical and chemical properties of the aerosols, will be compared with satellite measurements of the backscattering of solar radiation of ground-based measurements of the attenuation of solar radiation.
